Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
  • A61B5/6846—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be brought in contact with an internal body part, i.e. invasive
  • A61B5/6847—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be brought in contact with an internal body part, i.e. invasive mounted on an invasive device
  • A61B5/6851—Guide wires
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/01—Measuring temperature of body parts ; Diagnostic temperature sensing, e.g. for malignant or inflamed tissue
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/06—Devices, other than using radiation, for detecting or locating foreign bodies ; Determining position of diagnostic devices within or on the body of the patient
  • A61B5/065—Determining position of the probe employing exclusively positioning means located on or in the probe, e.g. using position sensors arranged on the probe
  • A61B5/066—Superposing sensor position on an image of the patient, e.g. obtained by ultrasound or x-ray imaging
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
  • G01R33/285—Invasive instruments, e.g. catheters or biopsy needles, specially adapted for tracking, guiding or visualization by NMR
  • G01R33/287—Invasive instruments, e.g. catheters or biopsy needles, specially adapted for tracking, guiding or visualization by NMR involving active visualization of interventional instruments, e.g. using active tracking RF coils or coils for intentionally creating magnetic field inhomogeneities
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
  • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
  • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
  • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
  • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
  • G01R33/34046—Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils
  • G01R33/34053—Solenoid coils; Toroidal coils
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
  • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
  • G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
  • G01R33/3628—Tuning/matching of the transmit/receive coil

Definitions

• the present application relates to interventional guidewires, and, more particularly, to such guidewires for use with interventional magnetic resonance imaging.
• iMRI Interventional Magnetic Resonance Imaging
• MR Magnetic Resonance
• Magnetic Resonance Imaging is one of the most important clinical imaging modalities.
• a significant advantage of using MRI in clinical procedures is that imaging via MR is conducted only using a strong homogenous magnetic field and radio frequency energy pulses, without the use of harmful ionizing radiation, such as with the use of X-ray angiography.
• MRI utilizes Nuclear Magnetic Resonance principles with gradient coil elements to provide spatial encoding, resulting in the ability to perform 3-D human body imaging with high soft tissue contrast (Lauterbur PC. NMR Imaging in Biomedicine. Cell Biophysics 1986; 9(1- 2): 211-214; Lai CM, Lauterbur PC. True Three-Dimensional Image Reconstruction by Nuclear Magnetic Resonancemaschinematography.
• MRI Three-Dimensional Nuclear Magnetic Resonance Shmato graphic Images of a Human Brain. Neuroradiology 981;21(5):239-244).
• MRI allows one to obtain information about various physical parameters such as flow, motion, magnetic susceptibility and temperature (Axel L. Blood Flow Effects in Magnetic Resonance Imaging. Magnetic resonance Annual 1986;237-244; Henkelman RM, Stains/ GJ, Graham SJ. Magnetization Transfer in MRI: A review. NMR Biomedicine 2001;
• MR guided interventions should be performed with devices free of ferromagnetic components, otherwise as one would encounter severe magnetic forces (induced displacement force and torque) on the device by the static magnetic field of the MR scanner and they would also cause image distortion due to the intrinsic susceptibility artifact (Shunk KA, lima JA, Heldman AW Transesophageal magnetic resonant imaging. Magn Reson. Med 1999;41:722-726).
• MR compatible and safe devices are not enough to perform vascular interventions with MRI. The reliable visualization of these devices in relation to the surrounding tissue morphology is also required.
• CT computed tomography
• a number of approaches have been developed for depicting vascular instruments in an MR environment. They can be broadly grouped into two categories: passive and active visualization.
• the tip or body of passive catheters is composed of either ferromagnetic or paramagnetic sleeves that produce susceptibility artifacts.
• Susceptibility markers should have a high magnetic moment to induce an adequate artifact at a variety of scan techniques and tracking speeds. In other words, they must have sufficient contrast to noise ratio (CNR) with respect to the background in order to distinguish the device in thick slab images.
• CNR contrast to noise ratio
• Active visualization relies on the incorporation of a miniature solenoid coil into the device itself (Dumoulin CL, Souza Sp, Darrow RD. Real-time position monitoring of invasive devices using magnetic resonance. Magn Reson. Med.
• Intravascular MR Tracking catheter preliminary experimental evaluation. Am J roentgenol 1995; 164: 1265- 1270).
• the coil is connected to the scanner via a transmission line such as a thin coaxial cable passing through the catheter and provides a robust signal, identifying the instrument location with high contrast.
• the tip of an active catheter can be visualized with high contrast by the incorporated coil on the tip.
• a solenoid coil is basic form of loop antenna element in which the wire is coiled in a helical pattern to create a cylindrical shape.
• Solenoid micro coils can be connected to the MR systems through the use of coaxial or twisted pair transmission lines, which may serve both detuning and signal transduction purposes.
• Loop antenna signal sensitivity for small-loop receivers falls off very rapidly (1/r , where r is the radial distance from the loop) (Balanis CA. Antenna theory. New York: John Wiley & Sons; 1997. p. 941).
• the opposed solenoid loop antenna is based on groups of helical loops separated by a gap region, with current driven in opposite directions in the helical loops on either side of the gap.
• the gap provides the small area of homogenous longitudinal magnetic field that makes it a good candidate for especially using as an imaging coil within and beyond the vessel wall. However, it has a small area of homogenous longitudinal coverage compared with the dipole antenna.
• a dipole antenna for iMRI applications can be a simple coaxial transmission line with an extended inner conductor.
• Dipole antenna sensitivity falls off as 1/r where r is the radial distance from the antenna center (Susil RC, Yeung CJ, Atalar E, "Intravascular extended sensitivity (IVES) MR imaging antennas.” Magnetic Resonance in Medicine, 2003; 50(2): 383- 390).
• Dipole antenna sensitivity can be improved by increasing the insulation layer
• the present application discloses a guidewire for magnetic resonance imaging with a single channel design to reduce complexity, while maintaining conspicuous both tip and shaft visibility under MRI.
• a guidewire body includes an antenna formed from a MRI compatible metal rod and a helical coil coupled together.
• the helical coil can have multiple windings without a gap between the windings.
• the rod passes through the windings of the helical coil and is coupled to the helical coil using a conductive joint.
• the conductive joint can be at a distal end, a proximal end, or both ends of the helical coil. When at a distal end, the conductive joint forms a conductive tip of the guidewire. Insulation can be positioned between the rod and the windings of the helical coil. The configuration allows visibility of the antenna along the shaft of the rod, but signals are suppressed where the rod passes through the coil.
• the tip visibility is enhanced because the suppressed signals between the tip and the shaft of the rod create a gap between the two.
• the gap increases visibility as it is easier to distinguish the distal tip from the rest of the shaft profile.
• the conductive joint is a solder joint with a semispherical shape in order to maximize conductive surface area and increase the tip visibility.
• the rod diameter can be reduced as the rod enters the windings in order to increase room for additional insulation.
• the additional insulation further reduces signal reception by the rod in the area of the windings.
• a guidewire for use with magnetic resonance imaging comprises an antenna formed from a combination of a rod and a helical coil.
• the coil defines an internal space
• the rod is positioned to extend axially through the internal space and is coupled to the coil using a conductive joint at an end of the rod.
• the conductive joint forms a tip of the guidewire.
• the guidewire has a null zone defined over an axial length between the conductive joint and a point proximal of the conductive joint. The null zone is operable to suppress signals received by a portion of the rod within the null zone, thereby producing a conspicuous distal tip signal.
• the null zone can produce a spatial separation between the distal tip signal and the shaft signal.
• the coil can have windings that are adjacent to each other over an axial distance corresponding to at least the length of the null zone.
• the guidewire can comprise a temperature sensor positioned in and axially movable relative to the guidewire.
• the temperature sensor can be configurable to monitor in real-time temperatures of interest along the guidewire.
• the temperature sensor can be configurable to measure for heating increases caused by defects in the guidewire.
• the guidewire can comprise a dedicated port formed in the guidewire into which a distal end of the temperature sensor is inserted.
• a distal end portion of the guidewire can be curved, and the helical coil can have a corresponding preformed curved configuration without gaps between adjacent windings.
• the helical coil can be preformed of a shape memory alloy into the curved configuration.
• the guidewire can comprise insulation in an annular region between the helical coil and the rod.
• the guidewire can comprise multiple layers of insulation separating the rod from the coil.
• FIG. 1 shows a distal end of a guidewire according to one embodiment.
• FIG. 2 shows a more detailed view of a distal end of a guidewire according to a second embodiment.
• FIG. 3 shows an extended view of a guidewire with a connector at a proximal end for connecting to a processing system.
• FIG. 4 is an illustration showing the guidewire with a conspicuous tip being visible.
• FIG. 5 shows another embodiment of the guidewire with a temperature sensor embedded therein.
• FIG. 6 shows a cross-sectional view of the guidewire taken along lines 6-6 of FIG. 5.
• FIG. 7 is a flowchart of a method that can be used to suppress portions of the guidewire in order to increase visibility of the tip.
• FIG. 8 is a schematic illustration of an interventional magnetic resonance imaging system that can use the guidewire described herein.
• FIG. 9A is an illustration showing a curved guidewire with a conspicuous tip.
• FIG. 9B is an illustration showing, on the left side, the guidewire as shown in FIG. 4 with a conspicuous tip indicated by the horizontal line, and on the right side, a conventional guidewire showing a lack of a conspicuous tip.
• FIG. 10 is a graph of normalized heating vs. time for a guidewire according to one of the embodiments.
• FIG. 11 is a graph of temperature vs. time for a guidewire according to one of the described embodiments, showing that there is no overheating problem.
• FIG. 12 is a magnified portion of the graph of FIG. 11.
• FIG. 13 is another magnified portion of the graph of FIG. 11.
• FIG. 14 is a graph comparing the magnitudes of guidewire heating in one of the described embodiments over three different test conditions.
• Fig. 15 is a chart summarizing the magnitude of guidewire heating for two different embodiments over three different test conditions.
• the current invention relates to the iMRI guidewires in which an antenna embedded into guidewire body is used for signal reception.
• a receiving antenna is positioned within the imaging volume that is used to detect the MR signal generated from the patient as the excited spins relax back into an equilibrium distribution.
• Embodiments described herein can be used for a clinical grade 0.035" multi purpose guidewire that can offer both precise tip location and distal shaft visualization,
• FIG. 1 shows a distal end of a guidewire 100 according to one embodiment including a single antenna formed from a rod 110 coupled to a helical coil 120 by a conductive joint 130.
• the rod 110 passes through the center of the coil 120 and couples to the coil at the tip 140 of the guidewire by the conductive joint.
• the conductive joint can be a solder joint or other means of coupling the rod to the coil.
• Soldering filler materials are available in many different alloys for differing applications. Examples include a eutectic alloy of 63% tin and 37% lead (or 60/40, which is almost identical in performance to the eutectic). Other alloys can also be used.
• the conductive joint 130 can have a semispherical shape so as to maximize a surface area to increase the signal intensity thereof. Other shapes can also be used. However, a large surface area can receive MR signals, which assists in making the tip 140 conspicuous on any resulting image.
• the coil 120 can be formed by a plurality of individual windings, such as winding 150, that can be tightly packed so that no gaps exist between the windings. By making the windings tightly packed, the received signal is significantly reduced for a portion of the rod 160 within the windings does not receive MR signals, while a shaft portion 170 of the rod outside of the windings does receive MR signals. This allows the tip 140 to be visible and separated from the shaft 170 by the suppressed area 160.
• FIG. 2 shows another embodiment of an end of a guidewire 200.
• the guidewire 200 is covered in an outer insulation 206 for safe insertion into a human body.
• a rod 210 extends longitudinally along the entire length of the guidewire and can taper in diameter as it approaches a distal end 216.
• a first inner insulation layer 220 is adjacent the rod 210 and surrounds the rod so as to suppress receipt of MR signals.
• the first inner insulation layer 220 may only be present in the area of a helical coil 230 and the tapered rod allows for the additional insulation in this area.
• a second insulation layer 240 can extend along the entire length of the guidewire.
• the rod 210 can be positioned with a tube 250.
• the tube can be made of conductive, non-magnetic material, such a metal alloy of nickel and titanium (e.g., Nitinol).
• the rod 210 can also be made of Nitinol or similar conductive materials.
• the rod can be coated with more conductive metals, such as with gold.
• the solder coupling is shown at 260 and electrically connects the rod 210 with the helical coil 230.
• the rod 210, coil 230 and tube 250 together form a single antenna and a single channel that receives MR signals and transmits the MR signals to a signal processing system for analysis.
• a second solder joint 270 can also be present at the proximal end of the helical coil. Frequency and phase information can be detected and analyzed in order to determine a position of the received signal and project an anatomical background image on a display so that a shaft and tip of the guidewire can be seen.
• FIG. 3 shows a view of an embodiment of an entire guidewire 300.
• the shaft 310 can be any desired length and includes a connector 320 for attaching to a signal processing system discussed below.
• the distal end 325 of the guidewire can be any of the embodiments described herein and is shown generically at 330.
• the helical coil 340 and solder joint 350 are similar to those already described.
• FIG. 4 shows a MRI image wherein a tip is shown as a dot centrally located and pointed to by arrow 410 is clearly visible and separated from a rest of the shaft.
• a suppressed region (seen as a dark space) between the tip and the shaft is due to the tightly wound helical coil and insulation within the coil.
• FIG. 5 shows another embodiment of a guidewire 500.
• a first portion of a rod 510 is not surrounded by the helical coil 520, while a second portion 530 is within the coil.
• the first portion of the rod 510 can have a larger diameter than the second portion 530, such that the rod tapers as it approaches the distal end 540 of the guidewire.
• the single channel guidewire includes an embedded port for a temperature sensor 550, such as a thermocouple, and a cable 560 (e.g., wire, fiber optic, etc.) attached thereto enclosed within an outer guidewire body 570.
• the temperature sensor is shown within the helical coil, but can be in any desired hot spot in which temperature information is desired.
• the guidewire can be any desired length and can be coupled via a connector 580 to a signal processing system, as is well understood in the art. Temperature information can be valuable to ensure that the guidewire does not exceed medical standards. Typical coil lengths can be around one inch in length. For longer coils (e.g., 2 inches), it was found that a small hole can be placed in the solder tip in order to lower permeability and increase magnetic field line density.
• FIG. 6 shows a cross-sectional view along lines 6-6 of FIG. 5.
• the inner rod is centrally located and surrounded by a first insulation layer, which can be only in the area of the coil, a second insulation layer, which can extend the full length of the guidewire, and the helical coil, shown as an individual winding.
• the third insulation layer covers the entire guidewire to insulate the guidewire from body fluids.
• FIG. 7 is a flowchart of a method for viewing a conspicuous tip of a guidewire.
• the signals are received at the tip of the guidewire using the conductive joint.
• process block 720 signals are suppressed over a length of a rod as it passes beneath a helical coil, while a remainder of the rod does receive signals.
• a gap is created between the tip and the shaft of the guidewire to allow easy visibility of both.
• FIG. 8 illustrates a system 800 in which the guidewire described herein can be used.
• the MRI system can include an MRI scanner 802, an active guidewire 804, according to any of the embodiments described above, and signal processing system 806 electrically connected to the active guidewire through the single channel described above.
• a tuning circuit (not shown) can be coupled to the guidewire as is well understood in the art.
• the tuning circuit can be incorporated as part of the signal processing unit 806 or can be coupled to both the processing unit 806 and the guidewire 804.
• the guidewire 804 is constructed to provide signal information indicative of a shaft portion of the guidewire and a distal tip portion.
• the system 800 can include a display 808 for visualizing the guidewire similar to FIG. 4.
• Additional components 810 can be connected for storage, if desired.
• a hot spot representing a portion of the device that reaches a greatest temperature located generally at the distal tip.
• this "hot spot” is repositioned along the guidewire proximally of the distal tip.
• measuring a real time temperature increase from RF induced heating under MRI with a fiber optic temperature probe is easier.
• the flexible distal tip is moved in ways such that it contacts surfaces (e.g., the surfaces of vessels, organs, etc.) frequently. If the hot spot is located at the distal tip, then the distal end of the fiber optic probe would need to be located at the distal tip.
• such a fiber optic has a GaAs crystal at its distal end, and this crystal would be subject to possible damage from the frequent contacts between the distal tip and adjacent surfaces.
• a distal tip with an internal curvature might not allow the planar distal end of the probe to be placed as close to the distal tip as desired. Rather, it has been discovered that the hot spot can be positioned proximally of the distal tip, taking into account one or more of the following factors: the profile of the inner rod, the thickness of the insulation layer(s), the inner and outer diameters of the solenoid coil, the solenoid coil length and wire diameter, the solenoid coil insulation material(s), the soldering locations, etc., to achieve the desired results for different guidewire configurations.
• FIG. 10 is a graph or heating profile of normalized heating over time for a guidewire with a temperature probe that is subjected to heating while the
• Point D on the graph corresponds to the distal tip.
• Point E hottest spot
• Point D has a higher temperature than Point D, and the highest temperature over the length of the guidewire.
• Point F is located at the proximal end of the coil 520.
• Points G junction where inner corewire enters hypotube
• H guidewire entry point into gel
• I MMCX connector
• the coil is constructed to have a closed pitch configuration. Stated differently, the coil is constructed so that adjacent windings are not separated by gaps. As best shown in Fig. 1, 2 and 5, the coils 120, 230, 520, respectively, are constructed such there are no gaps between adjacent windings.
• the closed pitch configuration of the coil helps to create a "null" zone in the received signal profile for the guidewire, i.e., because the side surface of the coil is substantially closed, the magnetic field is contained within the coil. If the windings are spaced from each other, then the magnetic field energy escapes and no null zone can be discerned.
• the left side of the figure is an image produced using a guidewire with a closed pitch coil and producing a conspicuous tip signal (i.e., the spot of brightness at the location of the added horizontal line) and a distinct shaft signal spaced from the tip signal by the interspersed null zone.
• the right side of the figure shows the image produced by a conventional guidewire without a closed pitch coil, which was aligned to be at the same position as the guidewire on the left side.
• the tip signal which should on the right side image appear in the area of the horizontal line is not readily discernible, or is at least not distinct from the tip signal.
• the surface area of the solder and the ratio of the solenoid coil diameter to the inner rod diameter ratio are factors that affect resonant LC properties of the structure. In the described implementations, these properties are optimized for 0.035 in diameter guidewires, but the same principles can be applied to guidewires of different sizes and configurations.
• the distal portion of the guidewire is curved or "bent" rather than straight. For example, as shown in the image of Fig. 9A, the distal portion 900 curves to the left looking in the distal direction from the shaft to the distal end.
• the shaft signal is marked by the numeral "2" in the figure.
• the tip signal is marked by the numeral " 1 " in the figure.
• a standard closed pitch coil in a straight configuration will deform when installed in a curved distal portion, causing gaps to occur between windings on the long side of the curve, which would lead to a poor or nonexistent null zone.
• a closed pitch coil suitable for a curved distal portion can be formed.
• the final curved geometry is carefully measured, and a metal mold for a coil corresponding to the final curved geometry is made.
• the coil can be molded to the correct final curved geometry, yet with the ability to deform during installation.
• the windings can be coated with parylene or other insulating material with a high dielectric constant.
• the maximum signal strengths for the distal tip (771) and the shaft (915) are of the same magnitude, and the distal tip signal is desirably strong.
• the guidewire has a dedicated port through which a fiber optic temperature probe or similar device) can be advanced and withdrawn along the guidewire shaft during a procedure.
• a fiber optic temperature probe or similar device This is especially useful in conducting testing, such as RF safety, before clinical use.
• the guidewire is arranged in a phantom and subjected to heating while the probe is withdrawn (a temperature probe pullback test). Areas of thinner insulation or other discontinuities, which might not be discovered through a visual inspection, create conspicuous hot spots that are easy to discern on a graph similar to Fig. 10.
• Figs. 11-13 are temperature profile graphs for a described implementation of the guidewire at different stages in a procedure.
• the measured temperature during insertion of the guidewire into a sheath rises rapidly and then reaches a highly uniform temperature (see also the inset magnified graph of Fig. 11).
• Fig. 12 shows the temperature profile after sheath entry and upon advancing to the left ventricle.
• a guidewire with a higher heating profile was used to demonstrate the measurement capabilities of the system.
• Fig. 13 shows the temperature profile for the guidewire in the area around the aortic arch. As noted, this profile shows that only fluctuations in the normal range occur during this phase of the procedure.
• Fig. 14 is a comparison of three different guidewire heating conditions: (1) an in vivo condition at a 45 degree flip angle, (2) an in situ condition at a 45 degree flip angle, and (3) an in vivo condition at a 70 degree flip angle.
• Fig. 15 is a chart summarizing a statistical analysis of the three conditions. In general, the results depicted in the figures show that the described guidewire implementations have comparable or better performance than conventional guidewires.

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• 2012
  • 2012-01-04 WO PCT/US2012/020139 patent/WO2012094365A2/en not_active Ceased
  • 2012-01-04 EP EP12732508.2A patent/EP2661221A4/de not_active Withdrawn
  • 2012-01-04 US US13/977,557 patent/US20130274591A1/en not_active Abandoned

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